The embodiment relates to a phase shift circuit and a backlight unit having the same.
A backlight unit provides light for image display to a display device such as a liquid crystal display device. The backlight unit comprises a light emitting unit and an inverter circuit. The light emitting unit emits light and the inverter circuit controls the driving of the light emitting unit.
The inverter circuit must supply voltage sufficient for turning the light emitting unit on and off. To this end, the inverter circuit comprises a transformer capable of boosting input voltage and a switching unit for controlling the driving of the transformer.
The light emitting unit may be divided into a plurality of groups. Each group can be separately driven by an additional control signal. Each group may be expressed by a single channel, and the inverter circuit may drive a single channel or multi-channel.
A multi-channel light emitting unit may be driven using a plurality of inverter circuits, which correspond to the number of channels, capable of driving a single channel. Further, the light emitting unit may be driven using an inverter circuit capable of driving multi-channel. In such a case, the inverter circuit can provide a control signal to the multi-channel by using one Pulse Width Modulation (PWM) module. The control signal output from the PWM module is provided to the switching unit that controls the driving of the transformer provided in each channel.
Each control signals provided from the PWM module to a plurality of channels may have the same phase. As illustrated in FIG. 1, control signals having the same phase may be simultaneously provided to a plurality of channels.
Further, each control signals provided from the PWM module to a plurality of channels may have different phases separated from each other without overlapping with each other. As illustrated in FIG. 2, after a control signal provided to a single channel comes into an off state, a control signal sequentially provided to another channel may enter an on state.
The PWM module provides the switching unit with a control signal having an adjusted duty ratio to control the brightness of light step by step, which is emitted from the light emitting unit. However, when the PWM module performs burst dimming control in the manner as described above, much noise may be generated or wave noise may be generated.